Field of the Invention
The present invention relates to an electrical discharge machine, and more particularly, to an electrical discharge machine with an adding device for a machining fluid used in electrical discharge machining.
Description of the Related Art
Wire electrical discharge machines are mainly used in production sites for metalworking and have been automated with the development of technology. Even in these days, however, replacement of consumption articles and maintenance of machines require human works for a certain time. If these works can be automated, the machines can be operated without rest at night and on holidays, so that the productivity can be improved.
Consumption articles in a wire electrical discharge machine include a tool electrode, filter, ion-exchange device and the like. A machining fluid can also be considered to be a consumption article, since it gradually decreases due to evaporation or adhesion to a workpiece during initial setup work. As a method for automatically adding the machining fluid, an arrangement may be provided such that the fluid level of a reservoir is monitored so that the machining fluid can be added when the fluid surface lowers.
As a technique for keeping the surface level of a machining fluid constant, for example, there is a method in which the amount of the machining fluid is measured and adjusted by detecting the machining fluid surface by means of a float switch. Further, Japanese Patent Application Laid-Open No. 2006-281395 discloses a technique for controlling the surface of a machining fluid to be at a certain level by comparing voltage across the following devices with a predetermined threshold and determining that the fluid surface is at a predetermined height. The devices include a machining tank having a built-in table on which a workpiece is placed and configured to store the machining fluid, a means for grounding the machining tank and/or the table, an electrode configured to detect the machining fluid surface, a voltage application device configured to apply voltage between the electrode and the grounded machining tank and/or table, and the grounded machining tank and/or table.
The height of the surface of the machining fluid in the reservoir can be controlled by applying the machining fluid surface adjustment method using the float switch or the like to monitoring of the change of the machining fluid amount in the reservoir. However, the total machining fluid amount in a wire electrical discharge machine comprising a plurality of reservoirs cannot be determined by this technique alone. In some cases, for example, the machining fluid stored in the machining tank may return and overflow after the exhausted machining fluid is added if only the surface of the machining fluid stored in each reservoir is monitored. If the machining fluid is added during machining, moreover, its quality may greatly change, possibly affecting the machining accuracy. These problems cannot be overcome by the above-described conventional techniques only.